Sweep limiter in radar indicating system



Dec. 22, 1953 R. B. TASKER 2,663,868

SWEEP LIMITER IN RADAR INDICATING SYSTEM Filed Feb. 21, 1951 8 sheets-sheet 1 Dec. 22, 1953 R. B. TASKER 2,663,868

swEEP LIMITEE 1N RADAR INDIcATINGvsYsTEM INI/EN TOR.

armena-V6 '0 ,em/Mana rasee@ Dec. 22, 1953 R. B. TASKER 2,663,868

swEEP LIMITER 1N RADAR INDIGATING SYSTEM Filed Feb. 2l, 1951 8 Sheets-$heet 3 TERHSMITTE@ 4 1 -29 ,em/Mavo e. rasee@ ,-f 5 2D INVENToR.

I l fr Dec. 22, 1953 R. B. TASKER SWEEP LIMITER IN RADAR INDICATING SYSTEM 8 Sheets-Sheet 4 Filed Feb.

Dec. 22, 1953 R. B. TASKER swEEP LIMITER IN RADAR INDICATING SYSTEM 8 Sheets-Sheet 5 Filed Feb. 2l, 1951 Sar M5553@ JW Dec. 22, 1953 R. B. TASKER EP LIMITER IN RADAR INDICATING SYSTEM SWE 8 Sheets-Sheet 6 Filed Feb. IIH

Dec. 22, 1953 R. B. TASKER 2,663,868

swEEP LIMITER 1N RADAR INDICATING SYSTEM Filed Feb. 21. 1951 A a sheets-sheet 7 Qi INVENTOR.

W ,em/Mavo 5. rasee@ Dec. 22, 1953 R. B. TASKER 2,663,868

SWEEP LIMITER IN RADAR INDICATING SYSTEM Filed Feb. 21, 1951 8 Sheets-Sheet 8 @fraai/EVS Patented Ecc. 22, 1953 SYSTE Raymond B. Tasker, Sepulveda, Calif., assigner to Gilfllan Bros., Inc.,

Los Angeles, Calif., a

corporation of California Application February 21, 1951, Serial N 0. 212,163

Claims.

The present invention relates to improved circuitry for producing two separate and distinct two-dimensional representations, displays or pictures on the screen of a single cathode ray tube, and in general relates to improvements in the cathode ray tube indication system useful in ground controlled approach (G. C. A.) aircraft landing systems of the type shown and claimed in the oopending application of Homer G. Taslrer et al., Serial No. 776,702, filed September 29, 194'?,

for Single Scope Two Coordinate Radar System.

In general, an object of the present invention is to provide en improved sweep limiter circuit for use in shaping and/or clipping the pattern of cathode ray tube displays, and in particular to shaping and/or clipping the two separate and distinct two-dimensional representations employed heretofore in ground controlled app-roach (G. C. A.) radar equipment.

In systems of this type it is desired to provide flexible, compact, light and inexpensive equipment for purposes of shaping and clipping the multiple pattern display from which an observer may accurately locate the position of an aircraft in space and with respect to a predetermined approach glide path and xed obstacles. This information is readily ascertained in that the two distinct representations, i. e., one showing the position of the aircraft as a function of its elevation and range, and the other showing the position. of the aircraft as a function of its azimuth and range, are correlated in that one of the representations lies directly above the other, with the range in each pattern being on the same scale and represented by the same horizontal distance in each pattern, as indicated in Figure 2.

An object of the present invention is to provide improved circuitry whereby the aforementioned results may be obtained with a relatively small number of component parts, such as vacuum tubes.

Another object of the present invention is to provide an improved indicating system of this character in which the functions of two multivibrator stages in prior art systems of this character are now produced by a single multivibrator stage, thus resulting in simplification and elimination of circuit components.

Another object of the present invention is to provide an improved system of this character in which the blanking or clipping, as it appears on the cathode ray tube, is cleaner and sharper and approaches the idealized condition.

Another object of the present invention is to provide improved which is capable of representation with range, i. e., Ae portion, unlimited, to thereby allow an observer to see an approaching aircraft earlier as it ies into the approach zone.

Another object of the present invention is to provide improved circuitry of this character which features the use of a blocking oscillator as an isolation stage between the source of triggering voltage and the pattern limiting circuit. in prior art systems of this character which used both an azimuth multivibrator and an elevation multivibrator, the region on the display in the vicinity of sweeps corresponding to zero degrees was not clearly defined, perhaps due to sporadic operation of these multivibrators in this transition zone where limiting was intended to be stopped. By effectively substituting the two multivibrators heretofore required by a single multivibrator, sharper denition is obtained in the representation in this region. It is therefore another object of the present invention to provide improved circuitry whereby this desirablev result may be obtained.

Another object of the present invention is to provide improved circuitry of this type characterized by its exibility whereby the representations produced may be adjusted, altered `or tailored to special congurations for unusual airport requirements. For example, in some instances, instead of having the usual preferred straight line approach path, obstacles to night of aircraft such as hills, mountains or the like may necessitate a curved or a dog leg type of glide path, and in such instances positions represented by diferent points on the representation should be accurately correlated with the particular glide path.

In general, the present invention contemplates an improved cathode ray tube indicating system in radar installations of the type in which two separate and distinct two-dimensional representations, displays or pictures are presented eiectively simultaneously on the screen of a single cathode ray tube, each of such representations being produced by sweeping a single cathode ray beam outwardly from different electrical centers. This is accomplished, using time sharing, by presenting one of the displays with a rst electrical center upon one portion of the screen, switching to a second electrical center and presenting the second display upon a second portion of the screen, and repeating further this accesos 3 procedure as a continuous cycle. By appropriate selection of the persistence time of the iluorescent screen of the cathode ray tube in accordance with the frequency of this cycle, both displays are made visible practically continuously, and hence may be viewed simultaneously.

Although the system is here described and shown as providing for two separate displays, it will be understood that certain aspects of the present invention may be applied equally well to the showing of one or more than two displays on one tube.

These broad general purposes are accomplished with the help of means which perform three more or less distinct functions, enumerated presently;

Firstly, after the presentation o one display is completed and before the presentation of' the next is begun, the zero, origin position or electrical center of the cathode ray beam is shifted on the screen by a controllable selected amount. This displacesone complete displayv relative to the other, so that the two displays do not overlap; or, so that they overlap in a manner and to an extent which can be controlled.. Secondly, and during the same time interval, the circuits which control both the intensity of the cathode ray beam and its position. with respect to its zero position are switched from control by input im pulses or sweep currents associated with one clisplay to control by impulses. or sweep currents associated with the other display. Thus the primary control circuits by which each display is reproduced need not be. basically dierent from the circuits by which such a display would normally be reproduced alone on a cathode ray tube. However, the. circuits. are modified in various rem spects, one type of modincation being the provision just referred to. for switching control from one. set of input signals or sweep currents to the other. And thirdly, in accordance with impor-- tant featuresV of' the present invention, novel means are provided for limiting the screen area occupied byv each of' the displays, by cutting off certain selected non-essential portions of them. This procedure, which we here call sweep limiting or pattern clipping, or merely limiting or clipping permits the two pictures to be so altered or tailored in shape that they can be fitted together more closely on the screen, while still avoiding anyV interference or overlapping be'- tween them, and Without distortion of those portions which are preserved.

Bythis expedient., complete information iurnished by the twoV radar systems, i. e., one scanning the aircraft approach zone in azimuth and the other in elevation, may be presented on the screen of av single cathode ray tube.. With the two representations in close juxtaposition they can be read accurately and virtually simultaneously by a single operator, who is then able to communicate rapidly the necessary information to the pilot of the aircraft, the image of which appears on both representations in relationship to predetermined glide paths or lines maintained on the screen by mechanical means.

The features of the present invention which are believed to be novel are set forth with parn ticularity in the appended claims. This invention itself, both' as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:V

Figure 1 is a schematic representation of por tions of a radar system embodying features of the present invention;

Figure 2 is a diagram of the combined azimuth and elevation displays produced in accordance with the present invention, using novel means for that purpose, and such figure includes the associated maps and flight tabs;

Figure 3 is a graphic representation showing the relationship of the azimuth and elevation antenna beam angle coupling voltages which are developed when and as the antenna beam is being scanned through space;

Figure 4 is a cycle diagram illustrating the time course of scanning and switching operations;

Figure 5 is a schematic perspective of azimuth and elevation antennas showing some of the associated equipment, partly in structural and partly in schematic form;

Figure 5A is a schematic representation for purposes of illustrating the time sequencev of the elevation blah-king gate, the azimuth blanking gate, and the Az-EZ relay gate;

Figure 6 is a block diagram of the circuits as"- sociated with the indicator tube for presenting a combination azimuth and elevation display;

Figure '7 is a schematic circuit diagram illustrating a circuit for establishing the electrical center of the cathode ray tube displays;

Figure 3 includes Figures 8A, 8B and 8C', each of which are shown on different drawing sheets,4 and it is intended that terminals having the same letters in these three figures be connected together for purposes of realizing Figure 8. Figure 8 when thus completed corresponds substantially to Figure l, but details of the sweepV limiter le are clearly set forth in Figure 8.

Figure 9 is a simplified schematic representation of portions of the sweep limiter circuit shown in Figure 8.

ln Figure l, the synchronizer l` serves to generate timing pulses which are used to time the operation of the trigger Shaper stage 2, the output of which is used to energize the transmitter modulator stage 3 which, in turn, causes the application of a pulse to the transmitter 4 to initiate its operation. This transmitter stage 4, thus pulsed at a constant repetitionrate of, for example, 2,000 pulses per second', consists of, for example, a magnetron oscillator with a characteristic frequency of about 10,000 megacycles. The output of this transmitter stage 4 is trans,- ferred to either the elevation (lill)v antenna I or' azimuth (Az) antenna 3, depending upon the position of the motor driven interruptor or radio frequency switch 6. The transmit-receive switch 5 (T. R. switch) prevents power from the trans-'- mitter l from being applied directly to the receiver 9. This transmit-receive switch 5, as is well known in the art, however, allows lowintensity signals', such as the train of resulting echo signals received on the antennas l', 8, to be transferred to the input terminals of' the receiver 9. This diversion of energy from the transmitter 4 to the antennas l, 8, accomplished by operation of switch f3, occurs at a rate of approximately two per second, so that in effect the combined antennas obtain four looks per sec'- ond of the space scanned. In other words,y the switch 5 is rotated twice per second, and while energy is being transmitted to one of the antennas l', 8, the resulting electromagnetic beam projected into space is caused to scan such space. The means whereby such scanning movement of the projected electromagnetic beam is obtained may be of the type described in the copending application of Karl A. Allebach, Serial No. 49,910, led September 18, 1948, now U. S. Patent 2,595,- 113, granted May 13, 1952, for Bridge Type Precision Antenna Structure, which depends ior its operation on the use of a variable wave guide type of antenna. This particular means, per se, forms no part of the present invention and, so far as the aspects of the present invention are concerned, the antenna scanning beam may be produced by moving the entire antenna through a relatively small arc of a circle. Actually, in effect, the azimuth antenna beam scans first in one direction and then in the other, waiting after each scan while the elevation beam completes a scan in elevation.

In initial adjustment of the antennas 1, 8, the elevation antenna 'I is servoed into position by means of the servo actuator lil, and data oi the servoed position of the elevation antenna 'I is transmitted by means of the servo data unit il to the rest of the system. Likewise, azimuth antenna 8 is servoed in azimuth position by means of servo actuator i2, and the position at which it is servoed is indicated to the rest of the system by data transmitted by the servo data unit I3. Once the elevation and azimuth antennas are servoed into position wherein their antenna beams scan the desired space, the antennas are left in that position.

While in any position during the part of the cycle in which the R. F. switch 6 (Figures 1 and allows the flow of radio frequency energy to the elevation antenna 'I the elevation antenna beam is electrically scanned in elevation. Position of the elevation antenna beam angle is measured by means of a variable capacitor 22, one plate of which is attached to the beam scanner of elevation antenna 'l and varied in accordance therewith, such capacitor 29 comprising one part of a capacitative potentiometer contained in the angle coupling unit 28, which may be of the type described in the copending patent application of George B. Crane, Serial No. 212,114, iiled February 2l, 1951. The angle coupler 28, when used with angle capacitor 2'1 generates a voltage 27A as shown in Figure 3 upon scanning movement of the antenna beam and of instantaneous value proportional to the elevation angle of the elevation antenna beam. Angle in azimuth of the azimuth antenna beam is measured by the angle capacitor 30 in azimuth angle coupling unit 3l, operating synchronously with the scanner of azimuth antenna 8. After transmission through the cable 36A (Figure l) from the antenna beam angle remoting assembly to the integrator assembly 31, the signal is reconverted to elevation angl-e voltage and azimuth angle voltage, as shown in heavy lines in Figure 3.

Also coupled to the scanner of the elevation antenna 7 is elevation blanker switch SQA which generates an elevation blanking voltage or gate so timed that its positive value corresponds to the time of effective scanning of the elevation antenna. The blanker switch 94E is similarly coupled to the scanner of azimuth antenna 8 and generates an azimuth blanking voltage which is so timed that its positive portion corresponds to the time of eiective scanning of the azimuth antenna. Relay switch SGF, operated substantially the same time as switch 94E and synchronously therewith, serves to generate an Az-EZ relay voltage or gate which is so timed that its positive portion begins at a time just prior to the beginning of the azimuth blankingi voltage and just after the ending of elevation blanking and which ends at a time just after the ending of the azimuth blanking and just prior to the beginning of the elevation blanking, as seen in Figure 5A.

The radar echo return, when received at the elevation antenna 'I or the azimuth antenna 8, is fed back through the R. F. switch and passed through the tune-receive switch 5 into the receiver 9. From the receiver is taken the video signal.

All the signals, i. e., triggering voltage, elevation angle voltage, azimuth angle voltage, elevation blanking voltage, elevation servo data, video, azimuth blanking voltage, Ae-EZ relay gate and azimuth servo data are variously transmitted to the remote site of the cathode ray tube indicators and their associated components. this remote site the display appears on an indicator 22 whose maximum range of display is 3 miles and on a second indicator 23 whose maximum range of display is 10 miles. described hereinafter as S-mile cathode ray tube and l0-mile cathode ray tube, respectively. Associated with the operation of the 3- mile cathode ray tube 22 and the lil-mile cathode ray tube 23 are a range mark generator 4| and a sweep limiter 40 which jointly serve both the S-mile cathode ray tube 22 and the l0.

mile cathode ray tube 23. A 3-mile sweep amplier 22C and a video amplifier 2D in addition serve the B-mile cathode ray tube 22. A l0- mile sweep amplifier 23C and a video amplifier 2l in addition serve the lil-mile cathode ray tube 23.

The general function of the sweep ampliiier 22C is to provide deection voltages across the magnetic deflection coils 22A, 22B of the cathode ray tube beam in the B-mile cathode ray tube 22. Also generated in the sweep amplifier 22C are a cathode ray sweep intensifying gate which is described later and a V-follower signal for the purpose of showing elevation position of the azimuth antenna beam in the elevation display and azimuth position of the elevation antenna beams in the azimuth display. 3-mile sweep amplifier 22C also generates a sweep limiter trigger, as well as an azimuth 30G-volt gate and an elevation 30G-volt gate for use by the sweep limiter 4R. Similar functions are provided for the 10-mile cathode ray tube 23 by the 10-mi1e sweep amplifier 23C which is not required to provide other signals to the sweep limiter 4U.

The function of the video amplier 20 is to apply to the 3-mile cathode ray tube 22 the range marks generated by the range mark generator 4I, the V-follower data and cathode ray sweep intensity gates generated by the 3-mile sweepA amplifier 22C, as well as the video detected in the receiver 9 and the pattern shaping voltages received from the sweep limiter 4i). rIhe video amplifier 2i) modulates the B-mile cathode ray tube 22 by means of signals applied to its cath-v ode, its grid and its rst anode. Similar functions in relation to the lil-mile cathode ray tube 23 are provided by video amplifier 2|.

Each cathode ray tube 22, 23 has two sets of magnetic deflection coils 22A, 22B and 23A, 23B,`

so arranged as to deflect the associated electron beam respectively parallel to two mutually perpendicular axes, the so-called time base axis which is generally, although not exactly, horizontal as viewed by the operator, and as shown in These are -modulating the sawtooth current through the time base (horizontal) deflection coil 23A with angle coupling voltages, the amplitude of the current decreasing slightly with increasing antenna beam angle. This has the eiect of tilting the range marks to the left as seen on the screen. The degree oi modulation is adjusted till the range marks are perpendicular to the runway axis on the map to thereby effectively move the antenna to a position on the runway axis from the position it actually occupies adjacent the runway axis where such antenna does not interfere with flight of the aircraft.

In Figure 2, a display or representation of both azimuth and elevation information is shown. The vertical dotted lines represent the range marks (actually continuous) produced by the cathode ray beam; the Eight solid lines are the maps, drawn on a single transparent sheet 6l superposed (optically or mechanically) on the face of the tube; and the dashed lines are drawn on the azimuth and elevation flight tabs S2 and 63, also transparent superposed sheets, one adjustable to pass through any desired touchdown point T1 of the azimuth display at any desired angle, and the other through the corresponding point T2 of the elevation display at any desired angle, The bright spots at P1 in the azimuth display and at P2 in the elevation display indicate an approaching aircraft which is little above and to the right (as seen from the runway) of the predetermined glide path X1 and X2. In both displays the axis of the runway (L1 and L2) appears horizontal. The lines U1, V1 in the azimuth display and the lines U2, V2 in the eleva tion display, shown in dotted lines are sci-called V-follower lines, the production and use of which need not be explained here,

It is observed that the azimuth display is directly below the elevation display, the range marks R1 of one appearingr as continuations of the range marks R2 of the other. This is a great convenience to the operator and tends to prevent any possibility of confusion, particularly -A when a number of aircraft are approaching the runway at the same time. Because of the continuity of the range marks, the azimuthA P1 oi the aircraft is always directly below the elevation image P2 of the same aircraft. This facilitates the identification of the two corresponding images from among a large number which may be visible. Also, if the azimuth image is partially obscured by the presence of ground reilections, it can be distinguished from the background more readily by reference to the elevation display, which is less subject to such disturbances.

Each display is generated as before by repeated sweeps of the cathode ray beam from the zero point O1 or O2, as the case may be, at a gradually varying angle which corresponds on an expanded scale to the momentary antenna beam angle. Following the variations in angie coupling voltages shown in Figure 2 which modulate the sweep voltages occurring at the repetition rate of the system, as described above, one display is presented completelyy the angle varying clockwise; then the other display is sirnln larly presented with the angle varying clockwise; then the first display is presented in the opposite sense, theangle varying counterclcckwise, and the second display is linally presented counterclockwise. A complete cycle of the antenna mechanism and associated circuit switch- 10 ing therebefore produces two complete scans of each picture.

Figure 4 shows a schematic diagram of the time relations involved in such a scanning cycle,V

which typically occupies a time in the order of one second. Forward progress of time is represented by clockwise motion about this diagram. The central circular region of Figure 4, marked N, shows the time schedule of the scanning operations of the two systems. Opposite quadrants represent complete scans by the same system, but carried out in opposite directions. The shaded arcas (each comprising roughly 10 of the complete 360 cycle) represent the periods during which the transmitter 4 is switched by the switch t in Figure 5 from one antenna to the cther Unshaded areas of region N represent the time periods during which one or the other of the antennas is in sending outl radio frequency pulses and receiving reflected echo signals from objects within the iield of coverage of the beam. Shaded areas indicate inactive periods, during which switching takes place, both antennas being` momentarily isolated from the transmitter and receiver.

The inner annular region M of Figure 4 represents the time schedule of the related azimuth and elevation displays, subject however to pattern clipping described later, and corresponds to the cyclical variation or Aa and El voltages represented in Figure 5A and applied to the control grid of the cathode ray tube, using the switches site. and 94E (Figure 5) for that purpose. Unshaded areas represent parts of the cycle during which this grid voltage is applied, shaded areas periods when this grid voltage vis ofi, making the tube inoperative.

The outer annular' region of Figure 4, marked L, shows .the time schedulel of current through the solenoids of a number of switching relays for eliecting time sharing. The relay actuating current can be obtained, for example, from a cam actuated switch @5F (Figure 5) operated in synchronisni with the anterma scanning mechanism.

`The switching mechanism will be clear from -Figure 5, which. is a perspective sketch, partly schematic, showing transmission line switches and also other elements of the switching system described above. All these elements are positively driven from a single shaft 89, one rotation of which corresponds to one complete cycle shown in Figure 4. Each element yon the shaft is preferably independently adjustable about the shaft axis, so that the relative timing of the various elements can be accurately established inaccordance with Figure 4.

The wave guide transmission line B0 leads from the transmitter l and receiving system, 9. A T-joint 65 divides this transmission line into two branches ii-@A and ilE, leading through switch assembly 6 to the azimuth and elevation antenna assemblies S and l, respectively. These `branches have suitably placed shutter slots which receive the rotating shutters 88A and 88E, respectively. These are mounted on the common drive shaft 89, driven by motor d, and have two blades each, arranged in opposite phase, so that when one antenna transmission branch is open the other will be blocked by'its shutter. The shutter blades' cover angles of approximately 100, leaving openings of 30, as required by region N of Figure 4.

The same drive shaft ililoperates the two antenna beam scan mechanisms, represented by the dotted lines 88K and 8SM and assumed to be of the construction shown in the above mentioned 1:1 Allebach .application .and built into the .antenna assemblies. In the showing of Figure :5 .the eccentric cams 132| A and 294i@ v.on shaft 2,39 Ioperate the beam scan mechanisms.

Since each of cams SiAa-nd SIE has one iobe, while its associated shutter 'SBA or SSE has two, one opening in the shutter will find the .antenna scanning in one direction, .the other in the .other direction.

'The azimuth and elevation .blanker switches :ME and 94A are shown schematically `in'ligure f5 .as cam actuated, ebeing operated by the two- 'lobed .cam 9.5, for .purposes of establishing .the gating voltages represented in Figure 5A.

The Az-El relay switch SAF is operated bycam 105| .on shaft :E8 to :control current to the circuit Aswitclnlng relays ,already referred to. The functions of the relay switches .operated ioy switch -SAF as vdescribec'l .above is indicated in Figure 6, which 'is a functional diagram showing some of the cir.- icui-ts .controlled by this switch and in greater de- `tan-some of the components shown in Figure 1l.

As illustrated, three separate -so-called Aar-EZ relays Ki Il, Klim, and Billed are Yused, each having two double throw switches m and with the exception .of `.relay Ki |64 which 'has `only switch n. The coils of all :three :relays are Acon.- vnected in parallel :between a source of positive Mortage .and switch SAF, which leads yto ground.

The switchn of relay Ki |34 seri/,es to .connect the positive plate supply voltage alternately .to the azimuth and elevation switchtubes in the pattern clipping circuit as .described below.

The sweep circuits, `shown in the upper part .of Figure 6, receive .impulses as `*before from the basic trigger, generated in synchroniser The trigger is fed through the delay multivibrator and blocking .oscillator stage 0 to the sweep multil:vibrator |1|-|. This generates a gate which is fed to the second mixer stage Ii lA to produce the f waveform iB .shown both in Figures 6 and 5A. This wave I HB comprises pulses of sweep -frequenc-y added to the longer Ae and EZ gates deueloped in the iirst mixer 1C. This composite wave 1|B is applied to the C. R. T. grid ||=2G, bringing .the tube up to the point of cutoff dur- -ing eachsweep. A negative gate is also generated in sweep multivibrator and fed to the -expansion .and time base modulators |22 and |23, and .from them through the expansion and time 'base amplifiers 121| and. |25 and -is applied as essentially trapezoidal waves of appropriate amplitude to the expansion deflection coils 22B and the `time case deflection coils 22A, respectively,

causing current pulses of linear Sawtooth -form in i;

the coils. Expansion and time base centering .circuits 126 and |21 (see below) .are also connected to the deflect-ion coils. The modulators 12: 2 and |23 receive angle coupling voltages via .Switches m and 1L, respectively, 1of relay Kimi. With the relay unactuated (as shown) the eleva- .tion coupling lvoltage :from I-tSE is connected through potentiometer |34 and switch fm to the expansion modulator |22; and through potenti.- ometer :|35 and inverter i3@ and switch n tothe time base :modulator i2 3, AAfter completion of the elevation scan, relay Ki `IBI is actuated by switch 100, breaking the elevation angle voltage coninfections* just described, and 4connecting the azimuth angle voi-tage from MSA through 4.potentiometer 3 .and switch to l the expansion modulator; .and through 4potentiometer i3?, inyerter 13| Yand switch .1L to .the time base modulator.

The potentiometers |34, |35, |135 .and ,|3351 con-d trol the amplitudes of the coupling voltages sunplied directly to the expansion .modulator and supplied V.indirectly Athrrmgh the inverters 'to the ytime basegmodulator. Thus'the degree of modu- `lation of the expansionsweep current, 'and hence the `.degree of angle expansion or" the display, can :be separately regulated for the azimuth displa-y by adjustment of the potentiometer i 3G and .for the .elevation display by adjustment ci potentiometer |34; andthe degree of modulation .0i lthe time base sweep current, `and hence the apiparent angle between ,the frange marks and the eti-me ibase G1K or .O aE, can jbe separately regu- Ilated for the Yazimuth display by adjustment oi potentiometer |31 and .for fthe lelevation display by :adjustment vor potentiometer i355. Th@ p0- tentiometer adjustments indicated in Figure A6 .can .be supplemented or Vreplaced by .many ldifferent types :0f electronic .control means, including the introduction, for example, of Vstage kof adjustable amplication between the coupling -iroiltage generators lA and i and the switches ofrelay Kil -:|01

The centering circuits me .and |27 in Figure 5 are individually capable of two separate adjustments, one eli-active when relay Ki lez is actuated Qazimuth display) and ,one when the relay is unactuated `(elevation display). One pair vof adjustments determines the vposition of point 01 in Figure 2 and `the other pair determines .point 0.2. Thus the origins of azimuth and elevation displays are separately adjustable, the centering circuits automatically responding to one .or other .set .of adjustments according as relay Ki H52 is actuated or unactua-ted.

.A schematic diagram of centering -circuitry for the expansion deilection coils is Ashown inFigures 6 and '7. The .deection coil 23B 'in Figurex'i 'is connected between a l55m-volt positive supply and two parallel circuits. Ione leading Vto ground through tube V-Hit, Ywhich -is the iinal stage of the usual expansion amplifier im, and 'the lother `leading through cholse coil LI 143| and centering tube V|| H to an 80G-volt positive supply. The first of these two `circuits yfeeds to deiiccticn coils 123B, the'periodically varying sweep producing current comp.onent,while lthe second circuit provides a relatively constant-but adjustable centering current component. The cathode resistor toi ,centering tube VH i1 is made up or" two parallel `corinept ed -potentiometers Ri-|58 and Rilie, the

Vmovable contacts of vwhich are connected re.- spectively Ato the normally closed and normally open contacts of switch m of relay 'KI |62. The switch farm is connected through grid resistor RI |51 to the tube grid. The grid bias, and hence the centering current through the tube and through the coil 23B, thus depends upon the position of rela-y switch m, being determined by @the setting of potentiometer RHSQ when relay KHDZ is actuated (azimuth display) and *by the sett-ing of potentiometer R||58 when the relay is not actuated (elevation display). 'The two dis.- plays are ytherefore separately adjustable as -to theirvertical position (expansion component) on .the indicator tube by means of the -two potentiometers.

Time base deflection coils 23A are provided with centering circuitry which is similar or identical to that of Figure v'i and functions i-n a like manner, controlled by switch n of relay 'Kl H22. In fact, by .appropriate changes of the numerals and lettering, Figure 7 may be vconsidered to illustratethe .timebase centering circuit. The potentiometers then provide separate adjustments of the azimuth and elevation displays with respect to their horizontal positions (time base component).

Thus, the centering circuits indicated in Figure 6 are separately adjustable for azimuth and elevation displays in both expansion and time base coordinates so as to produce adjustably spaced origins O1 and O2 of the two displays in Figure 5.

It is noted that the preferred interrelationship of the two displays (Figure 2) is such that the pairs of corresponding range marks of the two patterns lie in a single line, so that the two images P1 and P2 always lie in a line which is parallel to the range mark lines, specifically in this case one directly above the other. That relative relationship is due to the fact that the adjustments of the centering voltages and the adjustments of the angle coupling modulations of the time base sweep pulse amplitudes for both displays are such as to make both sets of range marks parallel to the line of relative displacement 0102 between the two origins of the displays. The time base sweep amplification (apart from this modulation) is the same for both displays, since the one time base amplifier E25 serves for both displays. Therefore, once the direction of the range marks is thus adjusted, corresponding marks of the two displays will be in a single line.

The azimuth display, which is preferably the lower one, is clipped, by means which include the pattern clipping stage dii, above a horizontal line HJ parallel to the runway axis and at a sufficient distance above it to allow for expected errors in the azimuth angle of approaching aircraft. In practice it is found that a satisfactory interval on the screen between clipping line and the runway axis X1 corresponds to an actual distance of about 2000 feet.

In the elevation (upper) display a section is cut out or clipped, by means which include the pattern clipping stage 40, below horizontal runway axis G2G and to the right of a short generally vertical line EF. This line is located just to the left of and parallel to the upper limiting sweep path 01H of the lower azimuth display. The

region thus eliminated from the elevation display corresponds to space below the runway level.

The small triangle O2EF which is retained below this level is well worth preserving, since it insures that an aircraft even at the point of landing T2, will appear well within the lower border of the display. The triangle OZEF is also useful in adjusting the electronic display, particularly to make that sweep path which corre-` sponds to a horizontal radar beam coincide with the ground line 02E' on map 6l. method of checking this adjustment, either in setting up the equipment or during its regular operation, is to compare the direct radar image Q of some natural or artificial object close to the ground, with the image Q1 of the same object reected in the ground surface. Under normal conditions correct adjustment is indicated if map line C2G passes between the two images Q and Q1, and is equidistant from them.

The action of the sweep limiter d, for purposes of clipping or limiting the cathode ray tube display, is now described in connection with Figures 1, 9 and 8 which includes Figures 8A, 8B and 8C. In general, there is provided a sweep limiting circuit for each one of the three-mile and ten-mile displays.

Assuming that all of the potentiometers in the sweep limiter are properly adjusted, the follow,- ing is a brief description of the operation of the same, it being noted that a more detailed de- An accurate 'scription of the circuitry thereof follows.

Aby operation of relay KI lll@ the Gate control The sweep limiter Ail receives as input signals from the 3-mile sweep amplier 22C, an elevation 300- volt gate, and 'azimuth 30D-volt gate, as well as a triggering voltage, both of such gates, of course, appearing alternately and occurring at a relatively low rate, whereas the repetition rate of the triggering voltages is the same as that of the cathode ray sweeps. It also receives azimuth angle voltage and elevation angle Voltage from the antenna beam angle trigger integrator assembly 37, such voltages being a measure of the scanned beam angle of the elevation antenna and of the azimuth antenna. The elevation-BOO-voltgate and the azimuth-BOO-Volt-gate are produced (Figure 6), which in turn is controlled by blanker switch SMF (Figures 5 and 6). Several of these signals are applied to the Elevation limit circuit, included in dotted lines in Figure 8A. By the control of the Elevation limit circuit the limitation of the elevation display may be adjusted. The Blocking oscillator type trigger circuit, indicated in dotted lines in Figure 8B, is utilized as a means of timing the pattern limiting voltage of the sweep. The signals from the Elevation limit circuit and Blocking oscillator are fed in parallel to two channels: one for the limitation of the 3- mile CRT display and the other for the limitation of the lO-rnile CRT display. The 3-mile CRT display channel consists of a Variable gate length multivibrator indicated as such on Figure 8B, a Gate control circuit and a 3-mile CRT Blanking gate multivibrator. The output of such Blanking gate multivibrator is applied directly through the video ampliier 20 without change therein which furnishes signals to the 3-mile tube 22. The 10-mile CRT channel consists of a Variable gate length multivibrator,

circuit and a l0-mile "Blanking gate multivibrator. The output of the 10- mile blanking gate multivibrator is aY blanking gate delivered directly through the video amp1ilier 2| without change therein which intensies 4the l0-mile CRT display.

potential level, an inverted and gated lo-mile elevation angle voltage is applied to resistor 249A from which the l0-mile elevation limit adjust potentiometer EMA derives the voltage for delivery to the l0-mile gate control circuit. From the .cathode of tube 2M, gated elevation angle voltage is delivered to the grid of tube 252. The bias of the cathode of tube 252 is adjusted by Elevation limit stop potentiometer 253, which functions to limit the value of elevation angle voltage beyond which no pattern. clipping will be derived. Signal at the anode of electron vtube 252 is delivered to the grid of tube Eil!! as inverted and limited elevation angle voltage which is used to set the level for the triggering voltage also applied to the same grid. Electron tube Zim lfunctions as an amplifier and the signal appearing at its anode is delivered to the anode of electron tube 208, of a blocked oscillator type trigger genera- -B-mile CRT limiting trigger l tor which .is normally n cutoff condition. The signa-l which `applied to .such 'anode of lelectron tube ,2106 Vis a trigger Vwhich 'operates .continuously at the .repetition rate of the rada-r system and in 'synchrcnism with it except .at such times as during the -elevation scan, the elevation angle voltage exceeds the critical value donned by the setting .of Elevation l-imit stop potentiometer 255. Either during the time `of azimuth scan when Ielectron tube 244 is not energized with plate veltageforduring the period of the elevation scan when the eleva-tion Yangle voltage vapplied .to the fgrid lof tube 24d is less than the .cutoff value determined 'by the cathode bias `potentiorneter 253 the trigger is applied to electron tube .290 to .re the 'block-ing oscillator, the output -o-f which appears across resistances .-21'4 and 215. The amplitude of such triggers is adj-usted by means of potentiometer 2id-for use with -mile CRT sweep limiting and by kmeans of potentiometer 21-5y :for ruse :with the l-O-mile CRT sweep limiting. The

taken from potentiometer 2id is applied to one side of the variable gate length multivibrator, composed of electron tubes 2 i8 and vFile to initiate a nip-flop operation by lcutting off the yconduction voi electron tube 219. The three-mile elevation limit `adjust potentiometer 25d has a signal derived from the Elevation limit circuit 'which is applied to `the grid of 'electron tube 222 which 'is gated on by the elevation-BOO-volt-gate applied to its anode. rPhe elevation angle voltage, thus inverted and gated, is applied by cathode coupling to electron tube 220. Also cathode coupled :to electron tube 2220 yis electron tube 221. On the grid `oi? tube 2-21 is applied azimuth 'angle voltage and on the anode 4of the same tube is ap. lied the azimuth 30G-volt gate. The azimutl-i angle voltage, so gated, is then cathode coupled to the I,cathode 'injector electron I:tube 220.. The cathode bias of electron tube 220 is determined by the 'combination -of potentiometer 239 which is labeled B-mile azimuth limit adjust #2, and potentiometer l2M) which is labeled -mile vazimuth limit adjust #3. The output of the cathode injector tube 22! alternately consists of elevation land azimuth signals. Potentiometer 291 whichis labeled f5-mile azimuth limit adjust #1 serves to @adjust `the time 'constant of the associated multivibrator grid circuit. The three .potentiometers .291., 239 vand 240, labeled respectively I-mile azimuth limit adjust #1, "3-mile azimuth limit adjust #2 and "Ii-mile azimuth `limit ladjust #3'may be variously adjusted so that the change in 1limiting which occurs with diierential :change in angle volt may be adjusted for optimum presentation, it being noted that the Elevation .limit stop .potentie-meter 253 is adjusted to determine .the angle voltage yat which clipping begins. The output of the variable gate multivibrator appearing at the anode of tube 219 is thus a positive voltage gate varying in time duration which decreases vwith increase in azimuth angle voltage, and with decrease in elevation angle voltage, in the vazimuth and elevation displays respectively. Such variable length voltage is applied to the differentiating circuit consisting of capacitor 236 and resistor 2?1 and grid conductance of tube 231, and thus the grid of tube 23'! of the CRT blanking gate multivibrator. rIube 231 is normally conducting. The negative pulse derived by the diiferentiator circuit 23B, 26% from the trailing edge of the variable gate voltage applied thereto operates to drive the grid of tube 23"! below the 16 4point ci conduction cutoff. 'fyical multivibrator action .results in a o-voltgate of which the heginning is ldelayedby the length of the variable ygating voltage :app-lied thereto. In the case p1'. the azimuth display the delay is variable from to v40 microseconds.; in the :case .of the elevation `disp-hay the delay is variable from 8 to vl0 microseconds. The produced blanking .gate is .applied `via the video amplilier without change therein to the :iirst 'anode of the S-mile .CRT 'in the form Vof a negative pulse. The signal thus :delivered to the first anode of Ythe 3mile `GRT functions to obliterate from the yS-rnile CRT display the remainder :of -reach sweep trace occurring after the .delay introduced by the variable gate length multivibrator.

:One of the features of the present invention resides in the :fact that, if desired, anunlimited :display of the 4azimuth presentation may be produced. This is accomplished by actuating the vswitch 302 which 'includes anorm'ally closed section Y:ill-.DA 'and a normally closed section 3MB. The :switch 3023A, a cutout switch, is in series with the 'El blanking switch SEA so as to prevent the transfer v'of the El portion of the wave shown in Figure 5A tothe control 'grid of the CRT whereby such tube remains dark, i. e., cut off, during the El antenna beam scanning. On the 4other hand, opening jof switch BlB .interrupts the :supply of anode voltage Vto tube 219A in the ill-mile variable gate length multivibrator, 'thereby preventing .its operation and hence preventing limiting of the azimuth presentation.

The following a more the sweep limiter 40.

1n Figures 8 randi? it is observed that the gated amplifier tube 200 is supplied with triggering Vvoltages from the sweep amplifier and is 'coupled to a blocking :oscillator stage 208 which serves :as an isolation stage. The output of this blocking detailed :description 'of oscillator. stage is transferred both to the S-mile and lO-mile circuits, but in the block diagram in Figure 9, for purposes of simplicity, it is shown -as being supplied only to the 3mile circuit which includes a timing multivibrator stage 21B, 2'13 anda blanking multivibrator 231, 1262.

'In general, the trigger applied to the gated ampliiier 200 initiates a gating voltage '300 -of a length which is variable and dependent upon the magnitude Aofi? the negative lgating voltage supplied to the timing multivibrator '218, 2 1-9 through the modulation amplifier 220. The voutput ofthe timing multivibrator 218, 219 is supplied Lto the blanking mutilvibrator 231, 262 which serves to change the polarity of the pulse, for `purposes of applying the same 301 to the iirst anode of 'the B-mile cathode ray tube. Such negative pulse 301 is of substantially constant. width, 'but displaced variable amounts along theA time axis, corresponding to the `trailing edge of the .positive pulse supplied thereto, and such vnegative pulse 301., while in existence, serves toblank the cathode ray tube, i. e., to darken the same.

For purposes of obtaining the variable gate 300, azimuth angle coupling volts or inverted elevation coupling volts, as the .case may be, `are transf-erred to the modulation amplifier 2-29, which serves to .generate the negative gating voltage 302., such .negative gating voltage 302 serving to terminate the positive gating voltage 300 gen-- erated in the timing multivibrator 218, 21.9.

The specific circuit :for accomplishing this general purpose is described in relationship to Figure 8. Triggering Vpulses applied :from the sweep amplifier 22C are transferred through condenser C-S50l to the control grid of the gated amplier tube 200. The cathode of tube 2li!) is connected to ground through the bias resistance and condenser combination 22|, 222. The anode of tube 200 is supplied with space current from the positive lead 29.5, such space current flowing through one of the windings .262 of the blocking oscillator transformer 281.

The blocking oscillator tube 228 has its cathode grounded and its control grid returned to ground through the transformer winding 209 and parallel connected resistance and condenser combination 2| Q, 2| The anode of tube 26S is connected to the positive lead 225 through the winding 222.

The output of the blocking oscillator appearing .across the winding 2|2 appears across the potentiometer resistances 2M, 2|5, the movable taps on whichrespectively serve to .supply adjustable potential pulses to the 3-mile and lO-mile channels 2| 6, 2|?. The S-mile channel 2 IB is the only one described in detail since it functions precisely as the lo-mile channel 2|, and any differences in operation of the same are mentioned herein.

The timing multivibrator includes the two tubes 2|8, 2|9, while the associated gate control circuit for the same for obtaining a variable trailing edge includes the three tubes 222, 22| and '222. connected through condenser 223 to the control grid of tube 2i9, such control grid being coupled through .the serially connected condensers 224, 225 to the anode of the tube 2| 8., which is of the pentode type and has .its cathode grounded. The anode of .tube l258 is connected to the positive lead 205 through the serially connected resistances 226, 22?. The screen grid is supplied with voltage from a voltage dividing circuit which includes the serially .connected resistances 228 and 229, the junctionpoint of which is connected to such screen grid.

Tube V2li! is of the pentode type and has its cathode grounded, and the anode of such tube is coupled through the parallel connected condenser 23B and resistance 282 to the control grid of tube 2|8. Tt is observed that the grid of tube 2'i3 is connected to the negative lead 23| through the isolating resistance 232. The screen grid of tube 21S Ais Iconnected .to .the positive lead 2|5 through the voltage dropping resistance 233.

The circuit thus far described, including the tubes 258, .2|.9, constitutes a multivibrator vfor generating square 'type gating voltages, the duration of which, however, Ymay be ,controlled by voltages supplied to the control vgrid of .tube '2|9 from the .anode of .tube 122D. rhesegating voltages controlledby the tube .229 :are transferred from the anode voi tube =2|9 through the serially connected resistances 2314 .235 and .oondenseri23 to the control gridof .the tube 23-7 inthe'blanking gate multivibrator circuit .231, .2.62, the connection and functioning of which vare described later after the Ifollowing description of rthe gate control fcircuit which includes the tubes .220, 22| and 222.

Only yone of the tubes 22|, 222 -is operative at any one particular moment, i. e., that moment when Veither the azimuth or elevation antenna is 'effective te transmit pulses andrreceive :resulting echo signals. Thus, when the azimuth antenna .-is effective, :plate -voltage in the .form -of van azimuth aga-ting voltage is applied to the anode -of tube 2 2| and when :the elevation antenna is effective for :thus purpose, iplate volta-ge inthe The variable tap on resistance 2|4 is vsistance 25|.

18 form of elevation gating voltage is supplied to the anode of tube 222. vThe cathodes of tubes 22| and 222 are interconnected :and returned to the negative lead 23| through a serial circuit comprising: the xed resistance 238, adjustable resistance 239, adjustable resistance 240 and xed resistances 24|, 222 and 2113.

Azimuth and elevation angle coupling voltages are applied to the control grids of the tubes 22|, 222 simultaneously with application of gating voltages to their corresponding anodes, but the elevation angle coupling voltage applied to the control grid of tube 222 is rst inverted, in a manner described in detail hereinafter, the inverter tube 224 being -connected for that purpose. The voltage thus appearing on the cathode of either tube 22|, 222, as the case may be, appears between .the control grid and cathode of the tube 220, since such control grid is returned to ground through the resistance 289. The anode of tube 222 is connected, for the iiow of space current, through resistance 29|)k to the positive 450-volt lead 211. The voltages thus developed on the anode of tube 222 are transferred to the `control grid of tube 2|9 through serially connected adjustable resistance 29| and xed resistance 222, so that the operation of tube 2|'9 is effected by the application to its control grid of, first triggering pulses supplied thereto from resistance 2|, and second, b y voltages in the form represented by the wave form 293 supplied thereto from the anode of tube 228.

More specifically, azimuth angle coupling voltages are applied to the control vgrid of tube 22| directly from the antenna beam angle integrating assembly 3l, through the resistance 245. -On the other hand, the elevation angle coupling voltages appearing at the output of the assembly 31 are transferred through 'the resistance 2% to the control grid of tube 2M, which serves essentially as an inverter tube for inverting the elevation angle coupling voltage and which also serves another purpose ras described presently.

Tube 246 has `its cathode returned to ground through resistance 24S, while the anode of tube 244 is connected .in the same manner as the anode of tube 222, i. e., to receive the positive .elevation gating voltage, whereby space current ilows through the tube 241i only during the time that the elevation antenna is eiective to ytransmit pulses and receive resulting v echo signals.

The elevation .angle coupling voltages thus appearing in ,amplied and inverted form on the anode .of tube 244i are .transferred tothe control grid of tube 222 vthrough .the series circuit which includes the xed resistances 2881, 249, adjustable tap on the potentiometer type resistance 252 and resistance till. It .is noted that one terminal of resistance 25|) is connected to re- `sistance 229, and the other one of its terminals is .connected to ground through the xed re- Theresistances 24B, 25|] and.25.| thus effectively .provide a voltage dividing circuit :from which vadjusted amounts of elevation angle coupling lvoltages, in inverted form, may be obtained and applied to the control grid of tube 222.

It .isfobserved that ,thecathoole of inverter tube .222 is connected to the control 1gridof the s ec- .ond l.inverter .tube .252, so that the uninverted velevation ,angle .coupling `voltage which appears across the .resistance .2.43 is transferred between the control .grid and .cathode Aof tube .252. The

`cathode ottube 2,52 irsconnectedtg the movable tap onthe resistance.2-53, kwhich forms .a portion nously with `said coupling means -for scanning r eac-h of 'said antenna beams lin space, means ide- 'riving a vcorresponding `azimuth angle voltage and an elevation angle voltage, the instantaneout magnitude of each of which is representative respectively of the position of the azimuth `and elevation beams, a cathode ray tube having a pair of quadraturely acting Vcathode beam deflee-ting means, two Vposition beam 'centering means alternately effective to move the cathode beam to different adjusted center positions,'

means operated synchronously with said transmitting sweep generating `'means for energizing said beam -de'flecting means to produce cathode beam sweeps, means operated synchronously with said coupling means to change from one of said centering means to the 'other centering means and fto alternately and synchronously Sapply said azimuth and elevation angle voltage to said sweep generating means, to thereby -Y'obtain alternate azimuth and elevation `'displays 'which are each expanded with reference to the space scanned respectively by said azimuth fand elevation antenna beams, said cathode ra'y 'tube 4having an intensity controlling electrode, a `single timing multivibrator circuit producing `gating voltage pulses in time relationship with triggerling of said transmitting means, means-alternately coupling said azimuth -and elevation angle voltages to said timing multivibrator circuit, 'said timing multivibrator 'circuit incorporating 'rneans 'for terminating each gating voltage pulse -produced thereby -at a time determined by the magnitude of said azimuth or elevation angle voltage, as the `case may be, a blanking gate generator coupled to said timing 'multivibrator circuit and .A

lfunctioning to initiate `blanking `voltages Iin accordanc'e with the trailing edge of said 'gating voltage pulses, and means applying vsaid blank- Ving voltages to said 'intensity controlling fele'ctrode.

2. rThe arrangement -se't forth .in claim 1 :in which means are provided for rendering inoperative said timing multivibrator in accordance with the magnitude of elevation angle voltage.

3. FIn a system 'of the character described, an 'azimuth antenna, fan elevation antenna, `energy transmitting means periodically vtriggered at 'a relatively high rate, means alternately 'coupling said transmitting Ameans to said azimuth antenna and said `elevation antenna at a relatively low rate to produce alternately a plurality of azimuth antenna beams and a plurality of eleva-Y tion antenna beams, means operating synchronously with said vcoupling means for scanning each of said antenna beams 'in space, means deriving a corresponding azimuth angle voltage and an elevation angle voltage, the instantaneous magnitude of each of which is representative respectively of the 'position of the azimuth 'and elevation beams, `a cathode ray tube having a 22 pair of Iquadraturely acting cathode beam deflecting means, two position beam centering means 'alternately effective to move the cathode beam to different adjusted center positions, sweep generating Vmeans operated synchronously with Asaid transmitting means for energizing said beam deilecting means to produce cathode beam sweeps, means yoperated synchronously with said coupling means to change from one of said centering means to the other centering means and to alternately and synchronously apply said azimuth and elevation angle voltage to said sweep .generating means, to thereby obtain .alternate azimuth and elevation displays which are each expanded with reference to the space scanned respectively by said azimuth and elevation antenna beams, said cathode kray tube having an intensity control electrode, means incorporating said 'intensity control electrode and operated synchronously with said transmitting means to blank selected portions of each azimuth and elevation display, and means effective to render the last mentioned means ineffective and to produce one of said displays with all portions thereof visible. 4. In 'a system of the character described, an azimuth antenna, an elevation antenna, energy transmitting mean-s rperiodically triggered at a relatively high rate, .means alternately coupling said transmitting means to said azimuth antenna and said elevation antenna at a relatively low rate to produce alternately a plurality of azimuth antenna beams and a plurality of Aelet/ation antenna beams, means 'operating synchronously with 'said coupling means for scanning 'each of antenna beams in space, means deriving a corresponding 'azimuth angle voltage and an elevation angle yoltage, the instantaneous magnitude of each of which is representative respectively of the position of the azimuth and elevation beams, a cathode ray tube having a pair ci raturely acting cathode beam dei'lecting means, two position beam 'centering means alternately effective to move the cathode beam to different adjusted center positions, sweep generating means operated synchronously with said transmitting means for energizing said beam deiiecting means to produce cathode lbeam sweeps, means operatedsynchronously with said coupling to-change-rom one of said centering mea-ns to the other centering 'means and to alternately and synchronously apply said azimuth and 'elevation angle voltage to said sweep generating means, to thereby obtain alter-nate azimuth and elevation displays which 'areleach expanded with reference to the 'space scanned respectively by said azimuth and "elevation antenna beams, said 'cathode ray tube having an intensity controlling electrode, a blocking oscillator ycircuit coupled to said enerizing means Yand functioning to produce triggering voltage pulses in timed relationship with appearance 'of said cathode beam sweeps, rendering said blocking oscillator circuit ective -in accordance with lthe magnitude of elevation ang-le voltage, a timing -niultiz'filnator cirf Acuit coupled to said blocking oscillator circuit for initiating gating voltage pulses, means coupled to and incorpora-ted in said 4timing multivibrator circuit for terminating each gating voltage pulse 'in accordance 'with the lmagnitude 'of said azimuth or-elevation angle `voltage, as the case may be, Ca blank-ing gate 'genera-tor circuit coupled to said timing multivibrator circuit for initiating blanking rgates in laccordance with 'timing of the 4trailing edge of said I'gating voltage pulses, and means 'coupling the output of said planning `said antenna beams in space, means deriving a corresponding azimuth angle voltage and an ele- Ytation angle voltage, the instantaneous magnitude' of cacho-:E which is representative respectively of the position of the azimuth and elevation beams, a cathode ray tube having a pair o' quadraturely acting cathode beam deilecting means, tvo position beam centering means alternately effective to move the cathode beam to dir".- ferent adjusted center positions, sweep generating means operated synchronously with said transmitting means oi energizing said beam delecting means to produce cathode beam sweeps, means operated synchronously with said coupling means to change from one oi said centering means to the other centering means and to alternately and synchronously apply said azimuth and elevation angle voltage to said sweep generating means, to thereby obtain alternate azimuth and elevation displays which are each expanded with reference to the space scanned respec by said azimuth and elevation antenna bea;1 said cathode ray tube having an intensity e. trolling electrode, means producing blanlring ga-uu voltage pulses and coupling the same to said electrode, said blanking gate pulse producing incorporating a multivibrator circuit .functioning to control the duration oi each blanking gate pulse, means rendering inoperative said multivibrator circuit in accorcia-nce with the magnitude of elevation angle voltage, and means controlling said multivibrator circuit in accordance with the magnitude or" azimuth or elevation angle volts, as the case may be.

6. in a system of the character described, a source ci triggering voltage pulses each of which appear in timed relationship with cathode ray beam sweeps, means coupled to said source for producing gating voltage pulses each cor espending to said triggering voltage pulses, said last mentioned means including only a single timing multivibrator, a source oi azimuth and elevation antenna angle voltage the instantaneous magnitude of which is representative of the angular position of an azimuth and elevation antenna beam respectively, meansr coupling said angle voltage source to said gating voltage pulse producing means, said gating voltage pulse producing means incorporating means for terminating each gating voltage pulse produced therein in accordance with the magnitude of said antenna angle voltage, a blanking pulse generator circuit coupled to said gating voltage pulse producing means and incorporating means for producing lolanking pulses in accordance with the trailing edge of each gating voltage pulse. Y

7. In system of the character described, a source ci triggering voltage pulses which appear synchronously with cathode ray beam sweeps, a blocking oscillator circuit coupled to said source, a timing multivibrator circuit coupled to said blocking oscillator circuit for initiating gating voltage pulses of variable length, a source of n el;

CTI

azimuth angle voltage, a Isource of elevation angle voltage, means coupled to said source of elevation voltage for inverting the elevation voltage to thereby produce inverted elevation angle voltage, a pair of switch tubes alternately eiective to couple said azimuth angle voltage and said elevation angle voltage to said timing multivibrator circuit, said timing multivibrator circuit comprising means whereby each of the gating voltage pulses produced thereby is terminated upon a predetermined magnitude of azimuth or inverted elevation voltage applied thereto, a second multivibratorV circuit coupled to said timing multivibrator circuit-and incorporating means for producinga blanking gate voltage pulse in response to the trailing edge of each of the first mentioned gating Voltage pulses, a cathode beam intensity control electrode, and means applying said planging gating voltage pulse to said electrode.

8. In a system of the character described, an azimuth antenna, an elevation antenna, energy transmitting means periodically triggered at a relatively high rate, means alternately coupling said transmitting means to said azimuth antenna and said elevation antenna at a relatively low rate to produce alternately a plurality of azimuth antenna beams and a plurality oi elevation antenna beams, means operating synchronously with-said coupling means for scanning each oisad antenna beams in space, means deriving a corresponding azimuth angle voltage and an elevation angle voltage, the instantaneous magnitude of each of which is representative respectively ci the position or the azimuth and elevation beams, a cathode ray tube having a pair of quadraturely acting cathode beam de- .ilectlng means, two `position beam centering means alternately effective to move the cathode beam to dierent, adjusted center positions, sweep generating means operated synchronously `with said transmitting means for energizing said beam deecting means to produce cathode beam sweeps, means operated synchronously with said coupling means to change from one of said centering means to the other centering means and to alternately and synchronously apply said azimuth and elevation angle voltage to said sweep generating means, to thereby obtain alternate azimuth and elevation displays which are each expanded with reference to the space scanned respectively by said azimuth and elevation antenna beams,

said cathode ray tube having an intensity control electrode, a blanking volt generator circuit coupled to said control electrode and functioning to apply blanking voltages to the same, said blanking volt generator circuit comprising a s gie multivibrator circuit operated in timed relationship with initiation of said cathode beam sweeps and producing gating voltage pulses, means for inverting elevation angle voltage to produce inverted angle Voltage, means responsive to the amplitude of azimuth angle voltage and inverted elevation voltage for controlling the duration of each of said gating voltage pulses, and means renderingsaid multivibrator circuit inoperative in accordance with the amplitude of inverted elevation angle voltage.

, 9.71m a systenrof the character described, an azimuth antenna, an elevation antenna, energy transmitting means periodically triggered at a, relatively high rate, means alternately coupling said transmitting means to said azimuth antenna and said elevation antenna'at a relatively low ratefto produce alternatelya plurality lci azimuth antenna vbeams and a plurality o ele- 

